The long-term objective of these studies is to explore the mechanisms involved in control of the metabolic systems and function of spermatozoa. The metabolic activity of sperm changes markedly in relation to its environment. This raises questions about the control processes which enable the sperm to adapt and retain its fertilizing capacity. The specific goal of the proposed studies is to clarify the role of the sperm adenyl cyclase in respect to sperm function and adaptability by investigating the properties of germ-cell adenyl cyclase system, which is distinct from other cyclase systems of mammalian somatic cells. In the seminiferous tubules of rat testis we found Mn 2 ion-sensitive, Mg 2 ion- and fluoride-insensitive adenyl cyclase developing during spermiogenesis. An adenyl cyclase of similar properties is present in epididymal spermatozoa. The stimulatory effect of Mn 2 ion on the tubular (presumably spermatid cell) and spermatozoal adenyl cyclase is augmented by Ca 2 ion. While in the seminiferous tubules the adenyl cyclase appears to be in the cytosol, in the sperm the cyclase system is firmly associated with membranes. We will attempt to establish the specific cell type where this distinctive adenyl cyclase is first synthesized. In our previous studies we found that the adenyl cyclase developing during spermiogenesis is remarkably soluble and extremely stable, in contrast to most adenyl cyclases in a variety of mammalian somatic cell types. Taking advantage of these properties of the tubular adenyl cyclase we propose the chemical purification and characterization of this enzyme. The molecular nature and the mode of activation of the germ-cell adenyl cyclase will be pursued. To accomplish the research objectives chemical, immunochemical and cytological techniques will be used.